1. Field of the Invention
The invention relates to controlled bonding of thermosetting fluoroelastomers to metal substrates with concurrent curing of said fluoroelastomers. More particularly, the invention relates to a method of controllably bonding fluoroelastomers directly to metal substrates while concurrently uniformly curing the fluoroelastomers without the use of added adhesive therebetween. The fluoroelastomers of this invention are typically relative chemically inert, thermally stable polymers, owing primarily to the strength of the carbon-fluorine bonds present in the molecules. Because of the thermal stability of these molecules, the fluoroelastomers are desirable in many applications which require elastomeric materials which will withstand high bulk temperature moduli. However, a great number of these applications, particularly in mechanical fields, require the elastomer to be used in conjunction with stiffening, or backup members, most often fabricated from metal, and hence require a method of bonding the elastomer to the metal member which will provide a bond capable of withstanding high temperatures and sustained or heavy loading. Particular examples include clutch plates and brake linings, where high friction coefficients result in very high ambient temperatures; many other examples will be apparent.
Unfortunately, the inherent properties of the fluoroelastomers, in particular chemical inertness, have made it difficult and, in some instances, impossible to effectively adhere uniform layers of these fluoroelastomers to a metal substrate, especially where high shear or impact strength is required in the finished fluoroelastomer-metal laminate, or where the finished laminate will be exposed to high ambient temperatures. The problem of bonding the ultra high temperature thermally stable thermosetting fluoroelastomers without at the same time reducing the uniformity of the layers thereof has been particularly troublesome.
2. Prior Art
Prior art methods which have been employed for bonding some types of fluoroelastomers to metal substrates have most commonly involved chemical bonding of the fluoroelastomers to the metal substrate with an adhesive bonding agent therebetween. These methods have limited application, however, since with both structural and non-structural adhesives, the bond achieved is not generally capable of withstanding sustained or heavy loading, or high ambient temperatures. Further, the adhesive bonding agent is highly subject to scuffing and wiping during molding of the product, which deactivates or destroys this agent, and therefore molding techniques and mold configurations for fluoroelastomer-metal laminates have heretofore been highly restricted.